Method of abrading titanium and titanium alloys

ABSTRACT

TITANIFEROUS METALS ARE GROUND MORE EFFICIENTLY, MORE RAPIDLY, AND WITH IMPROVED SURFACE FINISH USING A SILICON CARBIDE COATED ABRASIVE PRODUCT HAVING APOLYVINYL OR POLYVINYLIDENE HALIDE AS A SURFACE COATING, E.G., INCLUDED AS A PARTICULATE FILLER IN THE SANDSIZE ADHESIVE.

United States Patent U.S. CI. 51281 2 Claims ABSTRACT OF THE DISCLOSURE Titaniferous metals are ground more etficiently, more rapidly, and with improved surface finish using a silicon carbide coated abrasive product having a polyvinyl or polyvinylidene halide as a surface coating, e.g., included as a particulate filler in the sandsize adhesive.

BACKGROUND OF THE INVENTION This invention relates to the abrasion of titaniferous metal workpieces to obtain a desired shape.

In recent years titanium and titanium alloys have understandably increased greatly in popularity with aircraft manufacturers, since titanium is stronger, tougher, lighter in weight and more heat resistant than steel. Machining or grinding titanium alloys is, however, notoriously diflicult, and a wide variety of techniques have been tried without achieving any outstanding success.

As far as coated abrasives are concerned, titanium processors have recognized no significant difference between products having aluminum oxide. granules and products having silicon carbide granules, the two major industrial abrasive minerals. The Coated Abrasive Manufacturers Institute book Coated AbrasivesModern Tool of Industry, McGraw-Hill, New York, 1958, appears to lean toward the use of A1 0 for grinding titanium, although both A1 0 and SiC are suggested. To the same eifect, see US. Pat. 3,058,819, which stresses the utility of antiweld coated abrasive products made with aluminum oxide (and suggests the equivalence of products made with garnet and silicon carbide) for the grinding of titanium and other metals. US. Pat. 3,256,076 teaches that aluminum oxide coated abrasive products having a supersize of organic polymer containing chemically bound Cl, Bror S= are extremely effective in abrading ferrous metals; such products, however, are not significantly more effective than conventional products in titanium grinding.

Attempts have been made to improve the performance of both aluminum oxide and silicon carbide by using water floods to cool the grinding site, but no significant improvement has resulted. Dissolving trisodium phosphate in the water improves performance, but the. caustic effects on personnel and the deleterious effect on paint and bearing lubricants in the grinding equipment require many elaborate safeguards. In any event, floods are both expensive and inconvenient.

SUMMARY The present invention provides a simple, convenient, and inexpensive method of abrading titaniferous metals in which only a fraction of the coated abrasive material previously employed is used. Not only does the coated abrasive product remove more stock but the cutting rate is also increased; surprisingly, too, the finish is greatly improved over that obtained with a conventional product of the same abrasive granule size.

In accordance with the invention, titaniferous sheet ice stock, turbine blades for jet engines, etc., are abraded with a coated abrasive product in which the abrasive grain is silicon carbide, a polyvinyl halide being incorporated in the product so as to be present at the abrading surface. The polyvinyl halide is preferably included as particles in the conventional sandsize adhesive, but may also be incorporated in a separate film-forming supersize coat. In some instances the polyvinyl halide itself may 'be film-forming. The superiority of this method of grinding is surprising in view of the fact that an abradng process which is identical, except for replacing the silicon carbide granules with aluminum oxide granules, is essentially no more effective or efficient than a process involving conventional silicon carbide coated abrasive products.

DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS The invention will be better understood by reference to the following illustrative but nonlimiting examples, in which all parts are by weight unless otherwise noted.

EXAMPLE 1 Coated abrasive sheet material was made by applying a CaCO -filled phenol-formaldehyde make coat to a heavy duty resin-saturated drills cloth backing of the type described in US. Pat. 2,357,335 and then applying a conventional amount of Grade 60 silicon carbide granules. The make coat was precured in conventional manner, after which a phenol-formaldehyde resin sandsize composition was applied, the composition differing from the conventional sandsize by absence of the CaCO filler (normally present in an amount equal to 68% by weight of the total non-volatile content) and the presence of polyvinyl chloride particles (-20 mesh) in an amount equal to 70% by Weight of the total non-volatile content. The make and sandsize adhesives were then cured in conventional manner.

Endless belts, 3" x 132", were formed from the product described in the preceding paragraph and entrained over a 14-inch diameter serrated -durometer contact wheel driven at a speed of 5500 surface feet per minute (s.f.p.m.). A 6A1-4V titanium alloy test piece, having a Working face 7.25 inches x 2.062 inches, was urged against the contact wheel under a force of 19 pounds, the bar being moved in a vertical plane parallel to the direction of belt travel so that it traversed its entire 7.25-inch length every 6 seconds. The bar was then allowed to cool for one minute and the 6-second grinding stroke and cooling cycle repeated. The initial weight of the bar was noted, and every five strokes it was reweighed. The test was considered ended when the cut for each of any two consecutive weighings fell to 1.0 gram or less. The belt of this example cut a total of 83.9 grams prior to failure, whereas a control belt (identical except for the presence of CaCO filler and absence of polyvinyl chloride in the sandsize) cut a total of only 20.5 grams before failure. When the test was modified by cooling only every five strokes, and then for a period of 3 minutes, the control belt out 26.2 grams and the belt of this example cut 101.5 grams before failure.

The test described above was further modified by decreasing the belt speed to 2600 s.f.p.m. and cooling only every 10 grinding strokes, for a period of 3 minutes. The end point was considered to be reached when the cut for each of any two consecutive weighings fell to 2.0 grams or less. Conventional Grade 60 SiC belts, the PVC-filled Grade 60 SiC belts of this Example 1, and PVC-filled Grade 60 A1 0 belts (identical to the belts of this Ex- 3 ample 1 except for type of abrasive grain) were then compared. Results are tabulated below:

Belt: Total cut, grams Control-SiC 52.7 PVC-filled SiC 174.8 PVC filled A1 48.8

In field tests involving the abrasion of titanium sheet and titanium jet blades, it was found that PVC-filled SiC belts made from the product of this example cut from 200% to 300% as much as the best Grade 60 A1 0 or SiC belts previously available and that the finish on the blades was comparable to that obtained with conventional Grade 80 belts.

EXAMPLE 2 A quantity of conventional Grade 80 silicon carbide material was made on resin-saturated cloth backings in the general manner described in Example 1, except that the sandsize adhesive was omitted. A series of products was prepared by applying the same coating weight of sev- CaCO PVC phenolic resin,

weight ratio in sandsize:

Total cut in 12 minutes, grams 52:0:48 (Control) 37.0 42:10:48 40.7

It will be observed that belts containing at least 50% polyvinyl chloride by weight in the sandsize displayed a significantly higher average rate of cut than belts containing lesser amounts. The control belt was cutting less than 1 gram per minute and was considered at its endpoint, while most of the experimental belts were still cutting more than 1 gram per minute and were capable of further use.

EXAMPLE 3 A conventional Grade 60 cloth backed coated abrasive product (of the type used as the control in Example 1 above) was modified by applying, over the sandsize adhesive, a supersize composition consisting of a solution containing parts of polyvinyl chloride, 3 parts of 80% solids phenol: formaldehyde resin, and 60 parts of xylol, the total weight applied being grains of non-volatiles per 24 square inches. When tested at 5500 s.f.p.m. as in Example 1, belts made in accordance with this example cut 46.0 grams before failure, whereas control belts (no supersize) cut 20.5 grams. When tested at 2600 s.f.p.m. as in Example 1, belts made in accordance with this example cut 87.8 grams, while control belts cut 52.7 grams. Comparable improvements were shown in field tests.

EXAMPLE 4 Coated abrasive sheet material having the same type backing, make coat and Grade SiC abrasive particles as in Example 1, was sandsized with a composition containing, on a solids basis, 50% phenolic resin and 50% particulate polyvinyl bromide (PVB). Endless x 3" belts were formed from this material and a control (identical except that the sandsize was conventional CaCO -filled phenolic resin). Each belt was tested by entraining it over an 8 diameter -durometer serrated contact wheel, positioned above a reciprocating table, and driven at 4,667 s.f.p.m. Weighed titanium alloy (6A1-4V) test bars, 3" thick and having a 2 x 24" work face, were mounted on the table, which was then reciprocated at 20 feet per minute, the abrasive belt assembly moving downward (toward the table) 0.2 mil after every pass. The test bar was water-cooled and dried after each two passes. A strain gauge mounted beneath the table was connected to a power meter, the end point being determined when power consumption (above noload conditions) rose to 3.2 horsepower per inch of workpiece width, or 6.4 horsepower, at which time the bar was again weighed. When so tested, the belt of this example cut 118 grams and the control belt cut 49 grams.

Although the foregoing examples illustrate the presently preferred embodiments of the invention, other polyvinyl or polyvinylidene halides are also effective. For example, polyvinyl fluoride and polyvinylidene fluoride, although more stable than the corresponding chlorides or bromides, have improved the effectiveness of grinding titanium when included in or on a size coat, especially at high temperatures and/or pressures.

Abrading operations in which titanium sheets and castings are subjected to action of flap wheels using silicon carbide coated abrasive flaps, are also rendered more efficient when a polyvinyl or polyvinylidene halide is included in a size coat. Similarly, including polyvinyl or polyvinylidene halides in a size coat improves the effectiveness of abrading operations utilizing silicon carbide coated abrasive discs.

What we claim is:

1. A method of abrading titanium and titanium alloys comprising the steps of obtaining a coated abrasive belt having a drills cloth backing in which a hardened treating resin is present at one surface, and a hardened phenol-formaldehyde bond system comprising a make resin and a sandsize resin firmly anchoring silicon carbide particles to said backing, said make resin intimately contacting the treating resin at said one surface, said belt having, at its working face, a size resin containing at least about 5 0% by weight particulate polyvinyl halide or polyvinylidene halide,

driving said coated abrasive belt at a high rate of speed,

forcing a predominantly titaniferous metallic workpiece against said coated abrasive belt, whereby significantly more titanium is removed prior to dulling of said abrasive product than is removed by a product identical except for substitution of aluminum oxide as the mineral, elimination of the polyvinyl halide, or both.

2. The method of claim 1 wherein the coated abrasive belt passes over a contact wheel, adjacent the site of abradmg.

References Cited UNITED STATES PATENTS 3,058,8l9 10/1962 Paulson 51295 3,256,076 6/1966 Duwell et al 51-298 3,316,072 4/1967 Voss 51295 3,505,045 4/1970 Klein 5l298 DONALD J. ARNOLD, Primary Examiner U.S. Cl. X.R. 5l293, 295, 298 

